JOURNAL OF HORTICULTURE AND POSTHARVEST RESEARCH 2020, VOL. 3(1), 85-100 University Journal homepage: www.jhpr.birjand.ac.ir of Birjand Variability of physicochemical properties of ‘Deglet Nour’ date fruits collected from different oases in Djerid Region, Tunisia Rihab Taha1*, Ben Maachia Sihem2, Sindic Marianne3, Sahli Ali4, Namsi Ahmed2 and Messaoud Mars5 1, Institut Supérieur Agronomique, 4042 Chott-Mariem, University of Sousse, Tunisia 2, Regional Research Center in Oasis Agriculture of Degache, road of Tozeur Km1, 2260 Degache, Tunisia 3, University of Liege, Gembloux Agro-Bio Tech. Laboratory of Agro-Food Quality and Safety, Passage of the Déportés 2, 5030 Gembloux, Belgium 4, National Agronomic Institute of Tunisia, Rue Charles Nicolle, 43, 1082 Tunis, Mahrajene, Tunisia 5, U.R. Agrobiodiversité, Institut Supérieur Agronomique, 4042 Chott-Mariem, University of Sousse, Tunisia A R T I C L E I N F O A B S T R A C T Original article Article history: Received 23 June 2019 Purpose: Quality and physical characteristics of date palm changes during growth and maturation stages of fruits in main production Revised 7 August 2019 areas in the south of Tunisia. Research Method: The effect of Accepted 31 August 2019 season, ripening date and climatic conditions (temperature and Available online 30 September 2019 relative humidity) on physicochemical characteristics of fresh dates “Deglet Nour” grown at four different oases were evaluated using Keywords: multivariate analysis. Main findings: Dates from Traditional maturation Mountain Oases (TMO) had the highest values of length, width, weight, moisture content for the two seasons. Those from Modern oases Palm Plantation (MPP) had the highest values of fiber content, Phoenix dactylifera water activity, glucose and fructose in 2014. In 2014 and 2015, date physicochemical properties palm fruits of Modern Continental Oases (MCO) had the highest Tunisia values of sucrose. The lower values of the different parameters were registered for dates from Traditional Continental Oases (TCO). DOI: 10.22077/JHPR.2019.2569.1066 Meteorological data from the experimental station recorded higher P-ISSN: 2588-4883 temperature and relative humidity during fruit maturation (July, August and September) in 2014 compared to 2015. Results showed E-ISSN: 2588-6169 that the good quality of dates was obtained in oases TMO that had higher relative humidity and lower temperature compared to other *Corresponding author: oases (MPP, MCO, and TCO). Such changes may have resulted from Institut Supérieur Agronomique, 4042 earlier pollination and higher temperatures during the maturation Chott-Mariem, University of Sousse, period. Considering the two seasons 2014 and 2015, the highest Tunisia. thermal coefficients were observed in MCO (3726 and 3704, E-mail: [email protected] respectively) and the lower ones in TCO (3083 and 3025, respectively). Research limitation: No limitations were founded. © This article is open access and licensed under the terms of the Creative Commons Attribution License Originality/Value: Seasons and oases climate significantly affected http://creativecommons.org/licenses/by/4.0/ which the physical and biochemical quality characteristics of date palm permits unrestricted, use, distribution and fruits. This engendered in the longest maturity period recorded in reproduction in any medium, or format for any TCO. MPP where we recorded the highest spring temperatures, purpose, even commercially provided the work is properly cited. showed the shorted development cycle. Taha et al. INTRODUCTION South Tunisia is the main region producing date palm (Phoenix dactylifera L.) fruits (Besbes et al., 2009). More than 300 cultivars of date palm are present in Tunisia. Deglet Nour production in Djerid region is the most planted date palm variety (70% of the 5.9 million trees in all oases) because of its characteristics for both nutritional and sensorial properties (MARHP, 2016). In Tunisia, the export value of dates is around 486.5 million dinars annually (113.800 tons of Deglet Nour fruits). The Djerid region (governorate of Tozeur) is one of the important areas producing high quality of Deglet Nour fruit (Fruits, 2016). Cultivar growing in this hot arid region faces environmental stress such as drought, salinity, and heat, which limit tree growth and productivity (Youssef & Awad, 2008). One of the major problems in some zones of the Djerid region is a regression in quantities and qualities of Deglet Nour fruits. The most likely reason for regression in quantities and quality of Deglet Nour fruits is the impact of climate change and cultural practices (Shabana & Al Sunbol, 2007). Disturbances in the timing of fruit tree development have been observed as a result of recent climate change. The major effect of temperature should be the advancement of the phenological stages (the period of maturity will be advanced from 3 to 5 weeks), which can pose quality problems of the product by the advancement of the sensitive stages (Lavelle et al., 2008). High temperatures cause a high risk of scalding and disturbance of flowering, pollination and fruiting periods (Seguin & Stengel, 2002). The fruits of the date palm go through distinct development stages known locally as kimri, khalal, rutab and Tamar. Commercially, these fruits are consumed at khalal and Rutab stages as fresh fruits and at Tamar stage as dried fruits (Singh et al., 2012). The development duration of date fruits and their physical and chemical characteristics vary greatly with seasons and environments (Al- Farsi et al., 2007). Given the above, the objective of this study was to evaluate the morphological and biochemical properties of dates «Deglet Nour» from four oases at the Djerid region (southern Tunisia) during the maturation stages for two consecutive seasons. MATERIALS AND METHODS Experimental sites Samples of date palm fruits (Deglet Nour (DN) variety) were collected, during 2014 and 2015, at different development stages at four oases in Djerid region. - TCO: Traditional Continental Oases: three strata system: date palm, other fruit trees (pomegranate, apple, pear, lemon tree), and vegetable and fodder crops. It is characterized by a high density of palms with more than 200 trees/ha. The water cycle lasts eight days. - MPP: Modern Palm Plantation: monospecific cultivation: only date palm trees are grown. The distance between trees is about 8 m, giving about 150 palm trees/ha. The water cycle lasts ten days. - TMO: Traditional Mountain Oases: three strata system dominated by pomegranate and olive trees. The lower stage is occupied by a mixture of different vegetable crops: squash, parsley and forage crops. The number of palm trees is about 200 ha -1. The water cycle lasts six days. - MCO: Modern Continental Oases: three strata system where the density of palm trees is between 100 and 150 ha -1. The water cycle lasts four days. The differences between these oases are based on climatic conditions about their geographical positions, their mode of cultivation and management (Table 1). Irrigation system (submersion) and cultural practices are the same in these different oases. JOURNAL OF HORTICULTURE AND POSTHARVEST RESEARCH VOL. 3(1) MARCH 2020 Variability of physicochemical properties of date fruits Table 1. Average of heat units for 2014 and 2015 at different Djerid oasis (calculated from the data recorded by the meteorology stations at TMO, TCO, MPP and MCO) Date palm oases Heat Units (°C) 2014 Heat Units (°C) 2015 MPP 3456.44 3376.8 TCO 3542.54 3493.49 MCO 3726 3704.68 TMO 3083.52 3025.14 Table 2. Development stages recorded for Deglet Nour dates sampling Date of sampling June July August September S3 S4 S5 S6 Stage of sampling Kimri Khalal Rutab Tamar Phenological characteristics Dates of pollination and fruit maturity (Tamar stage) were recorded for all oases for the two seasons. Date samples Collection Fruit samples were taken monthly and for the different phenological stages (Table 2) according to the method of Girard (1980). Samples were taken from 5 different trees for each oases. Twenty homogeneous fruits of each sample were individually analyzed for morphological and physicochemical characteristics. Morphometric characteristics Fruit weight measured with an analytical balance, Fruit length and width were recorded for all sampled fruits at the different maturation stages with a vernier caliper. Measures were taken twice per each fruit on twenty fruits for each sample. Physicochemical characteristics The date fruit color was determined by a Minolta CR 300 color-difference meter (Ramsey, NJ) (C standard C.I.E. illumination, 0° viewing) (Artés et al., 2000). The CIE Lab coordinates (L*, a*, b*) were recorded. L* measured the lightness ranging from black to white on a scale of 0 to 100; a* the greenness to redness on a scale of -100 to +100; and b* measuring the blueness (-100) to yellowness (+100). When the a* and b* values increase, the color saturated, while when they approach zero they indicate neutral colors white, grey or black. The external husk color was determined as L*(lightness), or calculated as Chroma (C*=[(a*P 2 P + b*P 2 P)P 0.5P]) and Hue angle (H°= arctg b*/a*)). The pH values were determined using the method Girard (1980). To determine the fruit titratable acidity, 25 grams of date fruit were homogenized with 100 mL of distilled water. The mixture was heated into water bath at 90°C for 30min and filtered. The whole mixture was then filtered and titrated with O.1N NaOH with phenolphthalein as indicator. Titratable acidity was expressed as percent of tartaric acid. To measure water fruit content, 05grams of pulp were placed 24 hours in a stove at a temperature of 105°C.The water activity (aw) was determined by an aw-meter (Novasina Lab Master-aw, Swiss). The date palm samples were analyzed for acid and neutral detergent fiber by the method of Prosky et al. (1988), (AOAC, 1995) and insoluble fiber by the modified enzymatic-gravimetric method. The total sugars were determined by HPLC.